In the GMPLS network architecture, PCE, an emerging technology, has the main function of calculating the route of TE LSP based on the known network topology and restraint condition. RFC4655 and RFC4657 specifically describe the function and architecture of PCE as a path calculation element of GMPLS. The PCE architecture requires the PCC to be able to know one or more PCEs in a domain and the locations of other potential PCEs in other domains (for example, in the case of inter-domain TE LSP calculation). RFC4674 describes the detailed demand of PCE discovery mechanism. RFC5088 and RFC5089 respectively describe the mechanism of implementing the PCE automatic discovery by using OSPF and IS-IS route protocols. This mechanism allows the PCC to automatically discover a set of PCEs and other additional information for the PCC to select a PCE.
Currently, the network models to implement interlayer route calculation mainly comprise single PCE interlayer path calculation model and multiple PCE interlayer path calculation model. In this case, the multiple PCE interlayer path calculation models are further divided into two types, one with PCE communication and the other one without PCE communication. Typical interlayer route calculation model with PCE communication requires one certain PCE to possess visual capability only for the network topology of one designated layer (or several layers limited) and unable to possess visual capability for the network topologies of all the layers, which will be analyzed with FIG. 1 as the example. PCE Hi1 . . . PCE Him are PCEs responsible for the path calculation of upper layer and possess visual capability only for the network topology of H layer. PCE Lo1 . . . PCE Lon are PCEs responsible for the path calculation of lower layer and possess visual capability only for the network topology of L layer.
Before the present invention, the conventional implementation flow for the interlayer path calculation of this model is as follows:
1. LSR H1 sends a path calculation request of H1-H4 to PCE Hi1;
2. PCE Hi1 selects H2 as the ingress node to the lower layer and H3 as the egress node of the lower layer;
3. PCE Hi1 requests from PCE Lo1 to calculate an H2-H3 path;
4. PCE Lo1 returns H2-L1-L2-H3 to PCEHi1; and
5. PCE Hi1 calculates the complete path H1-H2-L1-L2-H3-H4 and returns the same to H1.
This flow exposes certain defects and shortcomings. According to the description of RFC5088 and RFC5089, currently, in the discovery information of PCE, the following are not indicated therein: what layer has the topology for which the PCE possesses visual capability; and what are the adjacent layers of this layer (generally, one certain layer has at most two adjacent layers which are located at its upper layer and lower layer). In this way, when LSR H1 is about to send a path calculation request to the PCE of its layer, it is impossible to learn in advance the adjacent layer information from the discovery information of PCE where its layer can calculate a cross-layer path and thus impossible to prepare in advance for whether to accept the cross-layer path which may be calculated.
In addition, since in the above implementation flow of interlayer path, the network topologies of H layer and L layer and the PCE used by each layer are separated, PCE Hi1, which as H layer can calculate the cross-layer path, can only send an L layer path calculation request to the designated L layer PCE Lo1 and thus cannot obtain the discovery information of L layer PCE Lo1 . . . PCE Lon (mainly including the location of L layer PCE and the layer information of PCE) by way of the flooding of the route protocol. And in terms of RFC4674, the implementation of the discovery requirement of PCE Hi1 as PCC for the L layer PCE, which is proposed by RFC4674, cannot be met inter-layers.